1. Field of the Invention
The present invention relates to a turbopump for conveying highly viscous substances, especially heavy hydrocarbons or petroleum, in which a liquid of low viscosity is mixed with the more viscous fluid being conveyed, in order to reduce the viscosity of the conveyed medium before entry into the pump. For this purpose, the turbopump comprises a pump with an inlet and an outlet, also a turbine with an inlet and an outlet, which are different from those of the pump, and which are fastened on the same shaft as the pump. In this turbopump, a vehicle fluid with a viscosity lower than that of the fluid that is miscible therewith is conducted under pressure to the inlet of the turbine. A portion of the vehicle fluid coming from the turbine as the solvent fluid, partially relieved of pressure, is admixed to the fluid in a chamber before entry into the pump, and thus the viscosity of the mixture is reduced. The mixture of solvent liquid and fluid is suctioned at the entry of the pump.
2. Description of the Related Art
A large proportion of the world oil reserves consists of heavy, viscous petroleum. As light petroleum is increasingly being exhausted, there exists a need for technologies to convey the heavy petroleum. Various methods for reducing the viscosity of petroleum have been developed in order to recover this petroleum, so that the petroleum can be conveyed with a pump that is in itself well known.
The GB-A-2 166 472 describes a method with a water jet pump and liquefying additives. However, it is pointed out that there is a risk of cavitation damage when this conveyance principle is used. This risk increases as the pressure of the pump increases and thus limits its field of application.
The references EP-A-0 322 958 and U.S. Pat. No. 4,749,034 describe the use of electrically driven pumps in a bore hole with an additional infeed of a solvent liquid and admixture thereof with the conveyed medium. However, electrically driven pumps have the disadvantage that they are unsuited for conveying highly viscous substances, since they tend to develop a large quantity of heat. The solution given for this in the EP-A-0 322 958 encounters its limits, however, if e.g. steam is used to heat the petroleum field. In addition, the cables for the electric motor are also sensitive to temperature.
The U.S. Pat. No. 4,056,335 describes the use of sucker rod pumps with simultaneous infeed of a solvent liquid. This is also an apparatus for recovering heavy petroleum, which reduces the viscosity of the fluid. However, sucker rod pumps can be operated only in vertical bore holes, and do not allow a horizontal orientation of the pump, such as is advantageous especially when conveying highly viscous petroleum.
The disadvantages listed here can be avoided by using a turbopump. These pumps are characterized by the pump being driven by a turbine which is seated on one shaft with the pump. The vehicle liquid in the turbine is wholly or partly admixed to the fluid.
The reference U.S. Pat. No. 4,086,030 relates to a turbopump and discloses an admixture of the vehicle liquid exiting from the turbine with the fluid exiting from the pump. This admixture takes place in a Venturi nozzle, such that the fluid surrounds the vehicle liquid exiting from a nozzle. This has a disadvantage that the admixture occurs only after the outlet from the pump. The viscosity of the mixture is not reduced before entry into the pump.
With the GB-A-2 057 058, the fluid is indeed admixed about a central jet of partially pressure-relieved vehicle medium of a turbine. However, the admixture of the two streams takes place before entry into the pump. This design is indeed especially suitable for conveying low-viscosity medium which contain gas, and to this extent shows that the viscosity of the conveyed mixture can be increased by the vehicle liquid. It is therefore unsuited for use as a turbopump to convey highly viscous media.
The EP-B-0 246 943, on the other hand, discloses a turbopump for conveying highly viscous substances. A component stream of the vehicle liquid is here conducted to the conveyed medium before entry into the pump chamber, with the objective of reducing the viscosity of the pump mixture. However, because of the annular infeed, the vehicle liquid is only partially mixed with the fluid.
The FR-A-2 656 035 also makes use of a process in which the vehicle liquid is fed into the fluid. It is especially suited for operating the pump in a horizontal position. However, it has the disadvantage that the highly viscous fluid is not conducted around the pump until the housing, before the vehicle liquid is admixed and the viscosity is thus reduced.
All previously known pumps consequently have significant disadvantages, which are undesirable for conveying viscous petroleum from deep bore holes which can also terminate in a horizontal position.